The current focus in the development of spark ignition (petrol) engines is to improve their efficiency. This can be done by down-sizing and/or turbocharging the engines. However, when this approach is taken, petrol engines have been observed to suffer from an abnormal combustion phenomenon known as pre-ignition, in which fuel combustion begins before the spark plug fires (see Manz, P-W et al, “Pre-ignition in highly turbo-charged engines. Analysis procedure and results”, 8th International Symposium on Internal Combustion Diagnostics, Baden-Baden, 2008; Zadeh, A et al, “Diagnosing engine combustion using high-speed photography in conjunction with CFD”, 8th International Symposium on Internal Combustion Diagnostics, Baden-Baden, 2008; Han, K-M et al, “3-D visualization of spark-ignition combustion: practical examples of flame propagation, abnormal combustion and controlled compression ignition”, 8th International Symposium on Internal Combustion Diagnostics, Baden-Baden, 2008; and Gerringer, B et al, FISITA Paper F2006P392.
Pre-ignition significantly increases the pressure and temperature of the unburned gas ahead of the advancing flame (see Kalghatgi, G T et al, “The nature of ‘superknock’ and its origins in SI engines”, I. Mech. E., onference on Internal combustion engines: Performance, Fuel Economy and Emissions, in London, Dec. 8-9, 2009; also Manz, P-W et al (above) and Zadeh, A et al (above)). This can lead to heavy knock (so-called “superknock”), another abnormal combustion phenomenon which could potentially damage the engine. It is therefore extremely important to reduce the probability of pre-ignition occurring in turbocharged spark ignition engines. Moreover as engines develop, with increasing levels of turbocharging in order to further increase efficiency, the problem of pre-ignition is likely to become more acute.